1. Field of the Invention
The present invention relates to solvent pumps which are used to pump adhesives to a site where bonding of two components can occur. The solvent can be used in conjunction with mass production apparatus which requires a minute quantity of such solvent to be delivered to the adhesion cite on a precisely timed repetitive basis.
2. Description of the Prior Art
In general, solvent metering pumps are known in the prior art. An illustration of one specific type of solvent pump which illustrates principles of prior art pumps is shown in FIG. 1 and is marked "PRIOR ART". This type of pump is manufactured by Valcor Engineering Corp. and is commonly known as a solenoid metering pump. A cross-sectional view of this type of pump is shown in FIG. 1. The pump 300 has a piston 302 which is pulled upward when a solenoid coil 304 is electrically energized. When the solenoid coil 304 is deenergized, a return spring 306 causes the piston 302 to move downwardly and return to its at rest position. The piston 302 moves inside a tube 310. The lower end of the tube 310 is enlarged to form a cylindrical chamber 312. The lower end of the piston 302 is enlarged to form a piston head 303. The piston head 303 divides the chamber 312 into an upper chamber 314 and a lower chamber 316. The piston head 303 contains a groove 305. A torroidal elastomeric pump ring 318 is contained in the groove 305.
When the solenoid coil 304 is energized the piston 302 is pulled upward. This in turn enables the pump ring 318 to form a seal between the piston head 303 and the wall of chamber 312. Fluid such as solvent 320 located in the upper chamber portion 314 is forced through the tube 310 and through outlet 322. At the same time, an inlet poppet check valve 324 is opened and solvent 320 is drawn into the lower chamber portion 316 through inlet 326. When the solenoid coil 304 is de-energized so that the return spring 306 forces the piston 302 back to its at rest position, the poppet check valve 324 closes by means of return spring 328 and solvent 320 is forced from the lower chamber portion 316 into the upper chamber portion 314 through a longitudinal slot 307 in the piston 302. The amount of solvent pumped during each cycle depends on the piston stroke length which can be manually adjusted.
In principal, most prior art metering pumps work along the principles of the illustrative example set forth above. The prior art works well for applications of solvent which is primarily in pure liquid form and does not contain any solid particulates. The prior art metering pumps do not work properly when they are required to pump solvents containing solid particulate adhesive matter due to the incorporation of check valves in the prior art designs. The solid particulate matter adheres to portions of the valve or valve seat, thereby interfering with proper opening and closing of the check valve assembly.This creates many problems in the operation of the pump. Since the check valve cannot close properly, there is additional pressure for excess fluid or solvent attempting to enter the pump from the major fluid or solvent reservoir. Since the adhesive causes the check valve to open improperly, insufficient fluid may be delivered through the pump. In addition, the improperly operating check valve may cause the timing of the entire pump to be off its set delivery timing and therefore solvent may be delivered to a site at an improper moment. While the check valve assembly has been illustrated in one position in the example set forth above, other metering pumps may have one or more such check valves at different locations throughout the pump. When solvent containing solid particulates comes in contact with one or more of such check valves, one or more of the problems set forth above will occur, thereby substantially interfering with the operation of the pump. Since such pumps are used on mass production machines which require the solvent to be delivered to a particular bonding site at a precise time during many repetitive cycles performed at high speeds, a problem can occur and not be noticed by the operator until substantial damage has been done to the pump, to parts of the assembly machine with which the pump is associated and to numerous parts being bonded together during the assembly operation.
There is no presently available metering pump which efficiently delivers solvent containing solid particulate matter for applications of use during a precise timing cycle requiring many rapid repetitions.